Schedule I - Condensed Financial Information of Registrant (Condensed Statements of Income) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Other operating expense									$ (1,238)	$ (1,232)	$ (1,236)
General taxes									262	252	234
Total operating expenses									(5,293)	(6,027)	(5,424)
Operating Loss	$ 245	$ 317	$ 204	$ 397	$ 273	$ 236	$ 235	$ 408	1,163	1,152	1,142
Interest income									12	5	3
Total other income (expense)									29	(16)	12
Interest on long-term debt									386	393	385
Intercompany interest expense and other									14	17	16
Total interest charges									396	407	398
Income Before Income Taxes									796	729	756
Income Tax Expense									271	250	302
Net income (loss) attributable to CMS Energy	$ 106	$ 148	$ 67	$ 202	$ 96	$ 94	$ 83	$ 204	523	477	452
CMS Energy [Member]
Other operating expense									(9)	(6)	(6)
Total operating expenses									(9)	(6)	(6)
Operating Loss									(9)	(6)	(6)
Equity earnings of subsidiaries									625	585	566
Interest income									1	1	1
Other expense									(9)	(20)	(8)
Total other income (expense)									617	566	559
Interest on long-term debt									134	150	148
Intercompany interest expense and other									3	2	3
Total interest charges									137	152	151
Income Before Income Taxes									471	408	402
Income Tax Expense									(52)	(69)	(50)
Net income (loss) attributable to CMS Energy									$ 523	$ 477	$ 452